1. Field of the Invention
The present invention relates to a solid-state image pickup device.
2. Description of Related Art
A back-side illuminated solid-state image pickup device that performs a global shutter operation has been proposed. For this technique, Japanese Unexamined Patent Application Publication No. 2012-248952 discloses a solid-state image pickup device in which a first substrate is electrically connected to a second substrate. In Japanese Unexamined Patent Application Publication No. 2012-248952, photo-diodes are disposed on the first substrate and a memory composed of capacitors is provided on the second substrate. Further, a global shutter operation is carried out by recording optical signals in the capacitors disposed on the second substrate.
Note that for increasing the dynamic range in a CMOS (Complementary Metal-Oxide-Semiconductor) image sensor, there is a method in which an optical signal obtained by a short-time exposure is combined with an optical signal obtained by a long-time exposure. When this method is implemented in a back-side illuminated solid-state image pickup device with capacitors disposed therein, it is necessary to provide the solid-state image pickup device with capacitors that are used to separately accumulate optical signals obtained by long-time exposures and those obtained by short-time exposures. Therefore, it is necessary to increase the number of capacitors. For example, in the case of Japanese Unexamined Patent Application Publication No. 2012-248952, it is necessary to add two additional capacitors corresponding to a clamp capacitance and an analog memory. Further, a transistor that is used as a switch for selecting one of these capacitors also needs to be added.